gpsmanshp at http://www.ncc.up.pt/gpsmanshp/ that "provides the means for creating and reading files in the ESRI Shapefile format for keeping 2 or 3 dimensional points and polylines". It is also based on shapelib.

the extension SpatiaLite to the database sqlite can read and write shapefiles from spatialite databases and can e.g. read a shapefile into a virtual table for convenient SQL querying. (It can, by the way, do the same for csv and txtr tables).

Shapetcl, a work-in-progress C extension that provides general-purpose read/write access to ESRI shapefiles. A draft of the API documentation is available here.